Many athletes, such as basketball players or soccer players, engage in their activities without any protection for their heads. As a consequence, head injuries, such as concussions, are not uncommon. By way of example, a basketball player could hit his or her head on the floor, two soccer players could hit their heads together, and so on. While these sports do not seem to necessitate full head protection, such as baseball batter's helmets, football helmets, bicycle helmets, etc., many of the most common head injuries are preventable.